Composition for cleaning metal



Patented Mar. 16,1954

COMPOSITION FOR. CLEANING Foster D. Snell, New York, N. Y.,- and William. H.

Stahl, Philadelphia, Snell, Inc., New York Pa., assignors to Foster D. New York, N. Y., a corporation of No Drawing. Application September 15, 1949, Serial No. 115;.952

17 Claims. (01. 252 1oo-) This invention relates to a composition for cleaning metal and more particularly to a composition which is particularly adapted for the cleaning of vertical surfaces of metal.

A variety of metal cleaning compositions have heretofore been proposed. Compositions have been disclosed which include a detergent or other material for removing oil from the metal surface and an acid for dissolving oxides, sulfides and other products of corrosion from the metal surface. The problem of retaining such compositions on vertical metal surfaces in films oi sufii ci'ent thickness to clean the surface has been I recognized and compositions have been prepared in the form of heavy pastes by including in their formulations various thickening materials, such as, boiled; starch, dextrin and various gums. Such compositions have been prepared in which bentonite, infusorial earth, tripoli and other earthy materials have been included for both their thickening efiect and their mild abrasive properties: These paste compositions have had the disadvantage of being diffi'cult to apply uniformly to a metal surface, particularly one of irregular contour, by reason of their heavy consistency and less satisfactory to apply than the more fluid compositions which fl'ow oil a vertical surface before the various products of corrosion are removed.

It is the object of this invention to provide an improved composition which is anefiicient cleaner for metal surfaces and which avoids both the disadvantages of the prior fluid metal cleaning compositions and those of the heavy paste compositions when used for cleaning vertical metal surfaces.

The metal cleaning compositions in accordance with this invention comprise four essential ingredients, an acid having an ionization constant within the range of about 1 '1 to about 1 10 a suitable surface-active agent, bentointo and water, in amounts and so proportioned to produce a thixotropic gel.

These compositions become fluid when subjected to mechanical work in applying them to a metal surface, but become gels when left at rest,

due to their property of thixotropy. Unlike the heavy paste compositions heretofore prepared for the cleaning of vertical metal surfaces, these compositions can be spread in a uniform, thin film over a vertical surface to be cleaned with relatively little labor, andunlike permanently fluid cleaning compositions they do not drain from the surface, but remain thereon to do an efliicient job of removing the oxides, sulfides and other products of corrosion from the metal. Further.

their fluidity during application to a metal: surface allows the surface-active agents and the bentonite to be fully effective in removing any oil film on the metal, even in crevices and grooves, and allow the acid. contained in their composition to react with the products of corrosion on. all parts of the surface, thus assuring a uniformly cleaned surface.

These metal cleaning compositions are the result of our discovery that within limited ranges of composition a thixotropic gel is produced by the four essential ingredients of our composition. We have found that the addition of certain surfaceactive" agents to mixtures of bentonite and; Water increases their viscosity or thickens them provided that too great an amount is not used. Mixtures of these three ingredients, over certain ranges of proportions exhibit the properties of a gel, but do not have the property of thixotropy'. 0n theother hand, mixtures of an acid, waterand bentonite can be prepared which are gels, but they do not exhibit the property of thi'xotropy. It is. only when all four or the ingredients are present that thixotropic gels can be produced, only when a suitable surface active agent is used, and only then when the proportion of each of these ingredients is within a critical range.

The acid which we utilize in our composition must have an ionization constant within the range 01': about 1 XIII- to 1 '10 to form a thixotropic gel. Any acid having an ionization constant within this range is suitable and the particular acid utilized will be selected on the basis of its efliciency in dissolving the products of corrosion of the particular metal or group of metals to be cleaned. Phosphoric acid, acetic acid and oxalic acid are examples of readily available acids having' ionization constants within the range of 1 1 5 to 1x112? which are suitable for use in our compositions. Strong acids, such as sulfuric acid and hydrochloric acid are unsuited for use incur compositions, si'ncethey will not-form compositions which are thixotropic gels.

Acetic and phosphoric acids can be used interchangeably, practically speaking, on a pound for pound basis. Acetic acid is less desirable than phosphoric acid in these compositions because of it'sorlor which is objectionable to many people. oxalic acid is of limited solubility, being soluble only to the extent of about 16% in water. However; it is solid in form and particularly useful in the preparation of compositions in accordance with this invention in the. form of dry powders to: which the: proper amount of water is added-at the point of use.

uses. Thus, compositions containing both oxalic and phosphoric acid are highly efficient for cleaning brass.

Bentonite, another of the essential ingredients of our composition, is a natural clay of the Pacific Coast States and is sodium montmorillonite. Of the many types of clay available, bentonite is the only one we have been able to locate which is suitable for use in the compositions in accordance with this invention. The standard bentonites are suitable for this use. However, we have found that a specially ground and screened, fine, granular bentonite such as, for example,

may be prepared by the procedure described in I U. S. Patent No. 2,036,617 to Bechtner and Hirschmann is particularly suitable for use in these compositions. This particular type of bentonite is not only advantageous in the rapidity with which it can be dispersed but also, in many cases, in that as much as less is required than of the standard bentonites.

To be suitable for use in the compositions in accordance with this invention, the surface-active agent must be water-soluble and must not react with the acid contained in the composition.

Further, it must retain its surface activity in an acidic aqueous medium and must have the synergistic property of increasing the apparent viscosity of a mixture of bentonite and water. Non-ionic and the cationic surface-active agents are, in general, useful in our compositions.

The anionic surface-active agents are, generally, not particularly suited for use in our compositions. Of that class, the ordinary fatty acid soaps are entirely excluded from use in our compositions since they ar reactive with the acid present. Further, the anionic surface-active agents cannot be used when a corrosion inhibitor is included in the composition, since corrosion inhibitors are themselves cationic in nature and therefore reactive with anionic surface-active agents.

Although certain of the anionic surface-active agents may be suitable for use in our compositions which do not contain a corrosion inhibitor, those which we have studied, including sodium keryl benzene sulfonate, in which the keryl group has an average molecular weight equivalent to the dodecyl group, sold under the trade-name of Nacconol NRSF' and sodium lauryl sulfate, sold under the name of Duponal ME, show only a very slight synergistic effect on the viscosity of a mixture of bentonite and water and have the objectionable property of causing air to be entrapped in the compositions to the extent of increasing its apparent volume by as much as one hundred per cent.

The surface-active agent which we utilize may b a single chemical compound or it may be one of the mixtures of compounds of closely related chemical structures characteristic of many of the commercially available surface-active agents. Further, we may use mixtures of two or more of the commercially available surface-active agents, which include two or more different compounds or groups of closely related compounds.

The degree of surface activity of the surfaceactive agent or mixture of surface-active agents which We utilize in our compositions need not be great. All surface-active agents of the nonionic and cationic classes meeting the qualifications of non-reactivity with the acid present and surface activity in an aqueous acidic medium,

tested in our investigation within the critical range of amounts set forth hereinafter, gave a gel-type product having thixotropic properties and smooth consistency, which showed no tendency to syneresis. The latter property is an important one, since syneresis will allow the aqueous solution of acid, surface-active agent and any other ingredients contained therein to drain out of the gel when deposited on a vertical surface and have the dual effect of decreasing the effectiveness of its action and of making the residual gel consisting principally of bentonite more difiicult to remove from the surface.

The variety of surface-active agents useful in the compositions in accordance with this invention is so large that for the sake of brevity, we desire to supplement this disclosure by reference to the discussion of the indicated classes appearing in the treatise entitled Surface Active Agents by Anthony M. Schwartz and James W. Perry, published 1949 by interscience Publishers Inc., New York, and to the review article entitled Synthetic detergents by John W. McCutcheon appearing page 811, volume 61, No. 5, of Chemical Industries, dated November 1947, published by Maclean-Hunter Publishing Corporation, New York. However, a few of the typical products falling onto the various classes which are suitable for our purpose will be discussed.

A nonionic surface active agent which is well suited for use in our compositions is a closely related group of polyoxyethylene ethers of alkyl phenols, which may be exemplified by the formula C10H21C6H4(OC2H4) 1201-1. A commercial product of this type is marketed under the name of Triton NE. A typical method of manufacture of non-ionic surface active agents of this class is the addition of ethylene oxide to a fatty alcohol, fatty mercaptan, fatty amine, alkyl phenol, thiophenol or substituted aniline. The number of moles of ethylene oxide added varies with different commercial products. Thus different commercial products of this class are produced by the addition of 6 moles, 7.5 to 8 moles, 20 moles and 30 moles of ethylene oxide, respectively, to one mole of dodecyl phenol. Related surfaceactive agents are produced by the condensation of 20 moles of ethylene oxide with one mole of oleyl alcohol and by the addition of 40 moles of ethylene oxide to one mole of castor oil, with the ethylene oxide forming an ether linkage with the ricinoleic acid residue at the 12 position. The production of non-ionic surface active agents by the addition of ethylene oxide to various molecules are shown, for example, in U. S. Patents 1,970,579; 2,213,417; 2,213,477; 2,129,709 and 2,205,021.

Other non-ionic surface-active agents which have been found suitable for use in our compositions are the fatty acid esters of the polyethylene glycols as described, for example, by U. S. 2,275,494. Commercial products of this class are sold under the trade-name Neutronyx and under the name Gycaid. The higher molecular weight" polyethylene glycols, particularly those having a molecular weight above 1000, are themselves non-ionic surface active agents suitable for use in our compositions. We have used the product known as Carbowax 1500 which is a blend of equal parts of a liquid polyethylene glycol having an average molecular weight of approximately 300 and a polyethylene glycol having an average molecular weight of 1340.

Other wetting agents of the nonionic class which are suitable are the anhydrosorbitol esters of fatty acids which have been solubilized by etherifying the free hydroxyl groups with ethylene oxide, such as, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate. The unetherifled anhydrosorbital esters of fatty acids which are water dispersible, such as sorbitan monolaurate and sorbitan monooleate, may be used in my compositions.

Cationic surface active agents which I may use in my composition include, for example, laui-yl pyridium chloride, cetyl pyridinium bromide, the coconut fatty alkyl dimethyl benzyl ammonium chloride, the product of the acylation of an unsymmetrical dimethyl ethylene diamine with a fatty acid chloride, such as, oleic acid chloride, having the formula Ci7H3sCONHC2H4N(C2I-I5)z, the tertiary amino alcohols, such as triethanol amine, and dibutylaminoethanol and the fatty acid esters of tertiary amino alcohols, such stearyltriethanolamine, oleyltriethanolamine and the stearic acid ester of dibutylaminoethanol.

The proportion in which each of the four essential ingredients is used in our composition is of critical importance. The tions over which each of the four essential in gredients may be used has been found to be substantially the same with all the combinations of acids and surface-active agents we have studied and we have found that the bentonite must be present within the range of about 2.5% to about 8.0% by weight of the total composition. The surface-active agent must be present in amount within the range of 2.5% to about 8.0%, by weight of the bentonite used. The acid must be used within the range of 2.5% by weight to the limit of its solubility in the water present but not in excess of 70%, by weight, of the total composition. Water must be present within the range of about 21%, by weight, to about 92.5% of the total composition, to make up the remain- .der of the composition.

Thus, the four essential ingredients of our composition must be within the following ranges to produce a thixotropic gel:

About 2.5% to about 8% by weight.

Bentonite Acid About 5.0% to about 70% by Weight. Surface active agent About 0.1% to about 0.8% Water to make 100%.

Phosphoric acid can be used over the entire range of 2.5%, by weight, to 70%, by weight, of the total composition. On the other, hand the limit of solubility of oxalic acid in water is about 10%, by weight, which limits the maximum per centage in which it can be used to about 9% by weight of the total composition.

While we have specified a variety of surfaceactive agents suitable for use in our compositions it is impossible to cover the entire field of such compounds which already number in the thousands, with additional ones being added continually. However, the suitability of any particular surface active agent can be readily determined by a simple test. Further, we have set forth the ranges of proportions over which the four essential ingredients of our composition by weight.

have been found to give thixotropic gels. Howexact range of propor- 6 ever, it can'be expected that the exact limits of the ranges, particularly those for the bentonite and the surface-active agent, may vary somewhat with certain combinations of acids and surface-active agents. In any case, it is desirable to determine specific proportions for any combination used by testing the effect of varying amounts of the surface-active agent on the apparent viscosity of the composition. Both the test of a surface-active agent for suitability in our composition and the determination of the optimum proportions of the ingredients of our composition will be illustrated with the following formula:

Lbs. Bentonite 6.9 Phosphoric acid 19.3 Water 73.3

The addition of, for example, 0.15 lb. of the surface-active agent comprising a mixture of polyoxyethylene alkyl phenols sold under the name of Triton NE will appreciably thicken the mixture. The mixture exhibits thixotropic characteristics. Increased amounts of the Triton NE increases the thickening up to about 0.50 lb. at which the thickening reaches a maximum. Further additions have the eifect of progressively thinning the mixture, so that when 1.25 lb. has been added the mixture is as thin as when no surface-active agent was present. Had this surface-active agent not exhibited a synergistic thickening of the mixture, and the resulting thickened mixture shown thixotropic properties, it would not be suitable for use in our compositions.

The exact amount of surface-active agent required to obtain maximum thickening varies with different agents and, in general, it is not desirable to utilize the amount which gives the exact maximum thickening, since the resulting manufacturing process becomes critical and diflicult to control. We prefer to utilize slightly less of the surface-active agent than the amount required for maximum thickening.

In formulating the compositions in accordance with this invention it is desirable to correlate the amount of surface-active agent used with the amount of bentonite present, in addition to stay ing within the critical ranges of proportions. Thus, in a composition containing 5.2% by weight of bentonite we have found that 0.2%, by weight, of Triton NE gives a thixotropic gel of satisfactory consistency. The same consistency can be maintained with a reduction in the amount of bentonite used, by increasing the percentage of Triton NE added to the composition.

In addition to the four essential ingredients which comprise the improved metal cleaning composition in accordance with this invention, it

- may contain other materials, such as corrosion inhibitors, oils and abrasive materials. Corrosion inhibitors which we may use are, for example, aliphatic amines or quaternary ammonium compounds. For example, monoethanolamine, diethanolamine, triethanolamine, lauryl. amine, and homologous compounds are suitable. Preferably, however, we use lauryl pyridinium chloride as the corrosion inhibitor in our composition.

The corrosion inhibitors are cationic surfaceactive agents. However, the amount required to inhibit corrosion is much less than that required to produce a thixotropic gel with bentonite and an acid. For the purpose of inhibitingcorrosion about 0.025%, by weight, to about 0.25%, by

weight, of thesaid composition; and, a watersoluble synthetic organicusurfaoe-active agent selected fromthegroup.- consisting of non-ionic and cationic surface active agents :and characterized byan essentially linear structure oneend of which is hydrophobic Pandvthe other, end of which is hydrophilic in.,character, Whichiisnot reactive with the said acidrin aqueo-uasolution, whichretains its surfaceactiyityin the presence oflthe said acid,- andwhich hasgthe characteristic of synergistically' increasingwthe apparent Viscosity of a mixtureof bentonite and water, in amount within the rangeof about=2.5% toabo'ut 8.0%, by weight, of thebentonite present, in the composition.

2. A composition in the-format a. thixotropic gel-for cleanin metal-having suspended therein an inorganic abrasive other. than bentonite-and consisting essentially of ..bentonite in amount within the range of about 2.5% by Weight, to about 8.0%, by weight, of theoomposition; water-within the range of about 21%, by weight, to about 92.5%, by-weight, of, the composition; an acid having an ionization constant within .the range. of about 1 ,10 to about 1 10 in amount on an anhydrous basiswithin' the-range of' about 5%, by weight, of the composition. to the limit of its solubility in thesaid'waten-but not in excess of about 70%,; by weight, of the said composition; and, awater'soluble synthetic organic surface-active agent selectedbfrom, the group. consisting of non-ionicand cationic surface active agentsand characterized by antessentially linear structure one en ofwhich, is hydrophobic and the other end ofuwhicht is hydrophilic in character, which is not reactive with the said acid in aqueous: solution,;which retains its surface activity in the presence'of the said acid, and which has" the characteristic of-synergistically increasing the apparent viscosity of a mixture of bentonite and water, in amount within the range of'about 2.5% to about 8.0%, by weight, of the bentonite present in the'composition.

'3. A compositionain the formof a thixotropic gel for cleanin metal consisting essentially of bentonite in amountzwithin the; ran e of about 2.5%, by. weight, to, about 8.0%,,yby; weight, of

the composition; water within the rangeiof about.

21 by weight, to abo'ut92:5%,. by weight;,-'of the composition; anixacidi havin qan' ionization constant within the range of: abOnt I'XJO- to about 1 10' in amount on an'anhydrous basis within the range of about 5% by'weight, ofuthe composition to the limit of its: solubility. in. the

- said water; but not in excess of: about 70%,- by

weight, of thesaidt composition; a water-soluble synthetic organic surface-active agent, selected from the group consisting of non-ionic anclcationic surface active agents and characterizedby anessentially liear structure one 7 end of which is'hydrophobic and the other-end'ofwhich-is hydrophilic in character, which isnot reactive with the said acid in: aqueous so1ution,'which= re-- tains its surface activity in the-presence of the said acid; and which has the characteristic of synergistically increasing the apparent viscosity of a mixture of bentoniteand Water, inamount within the rangeof about 2.5%- to about 8;0%, by weight, of thebentonite presentinthecomposition; and a corrosion inhibitor in amount'withinthe range of about, 0.025% by weight; to a'bout 0225 l by weight; of the composition.

10 4..eAldmpowdenadaptedito,formaatthixotronic gel'suitable for cleaning metal when intimately admixedwith an amount of, waten within the range of.-about.,211.0.%,,,byweight,-,to;abdut,92}5 by; weight, ,ofithe-finai-composition, ,consisting ,essentially, of bentonite gin ,amount-within the range of,- about 2.5 a by, .weight', .toihabo'ut; 8.01- by weight, of, the final composition; ;--an -acidhaying an ionization oonstantwithin the range of about 1 1o+5 t about ,1= ,1o 2"whioh is solidi-at (normal room temperatures: in amount:- on: an vanhydro basis withinthemangeqf aboutr576 Weight}, of the composition =to the limit; or; itsisolubility, in

the} said i water; but not intexcess on about: 70%.

by weight, of the said composition;and-amatersoluble synthetic organic surface-activesagent selected from the group consis'tingaof, non-ionic and, cationic, r surface. active: agents.- and-characterizedby an essentiallyllinear structureonennd of'which is hydrophobic andv thetotherl endtof which is hydrophilic inlcharacter, :whichiSfiSOlid at normal room temperatures, which, isjnoto-reactive with the'said acid in:aqueous/solution, which retainslits surfaceactivityain the presence ofthe said acid and-which haLstheicharacteristic of synergistically;increasingtheapparenhviscosity ofa mixture of bentonite andiwater,:-,-in amount within the range of about r2 .5,% =toabout 8.0%, ,byweight, of, the ,bentonite present in the composition.

5. A t composition inathe iform of a thixotropic gel for cleaning metal consisting essentially of bentonite in, amounts-within the; range of-about 2.5%, by weight, to about,-8.0%,,;gby, we ight,:-of

the-composition; water within the 'rangetot, about 21%, by, Weight, to about 925%, by-;weight,,,of the composition; an acid having-sang ionization constant within the range of, about-21x1 0* to about 1 10- inamountonion anhydrous basis within the rangeof about-,5 bytweight, offthe composition to thelimitor its solubilityv irrthe said water, vbut -note in 2 excess of? about- {by weight, ofithe said composition; and a noneionic surface-active agent in amount within the range by weight,- to, about: 8.0 by :veig-ht, of, the ,bento-nite;-p resent in the; composiion.

62 A: compcsitioniin ithegform of :ai thixotropic gel for\- cleaning;- metal consisting; essentially of bentonite in amount; within: the range of: about y w i hmtoabout; 8 .O%,,;,by weight; of the composition; waterv within:the' rangeiofiabout 21%, by weight, to-abouts92:5% ,,-by:weig ht;i0f the composition; phosphoric acid in: amount; on

. I an anhydrous basis:- within: the rangezi-ofir about 5%; .by weight, toaboiit?70%;;1by-weight of: the

composition; 1 and a roiycxyethylene 'ethen'ofz an alkyl phenol Within thewran-gewofi about. 2.5.=,%', by weight, to' about:8z0 bytweight;ioithebentonite present in the composition;

7. A 'scomposition:inuthe 'form of a1 thixotropic .gel for cleanin metal consistingoessentiallyeof bentonite in amount: within the rrangerof about 2.5 by weight, to aboutkBzG %r;byrweight, ofxt-he composition;-: water within; th ra-nge oft-about 21%, byxweight, to about 92:5 byeweight of the composition; an acid having-1' anwionization constant within the rangeaof about-1 -10 to about .1 .10.- inlamou-nti on, antanhydrousqbasis within the range of-about ,5 %-,i-by ;-weight;lof the composition to the limit of its solubilityiinfthe said, water, butnot in excessioii about .70% by weight,,, of] the. c, said. composition.- and' a. catonic '11 weight, of the bentonite present in the composition.

8. A composition in the form of a thixotropic gel for cleaning metal consisting essentially of bentonite in amount w.thin the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of the composition; phosphoric acid in amount on an anhydrous basis within the range of about by weight, to about 70%, by weight, of the composition; and a non-ionic surface active agent within the range of about 2.5%, by weight, to about 8.0%, by weight, of the bentonite present in the composition.

9. A composition in the form of a thixotropicgel for cleaning metal consisting essentially of bentonite in amount; within the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of the composition; phosphoric acid in amount on an anhydrous basis within the range of about 5%, by weight, to about 70%, by weight, of the composition; and a cationic surface active agent within the range of about 2.5%, by weight, to about 8.0%, by weight, of the bentonite present in the composition.

10. A composition in the form of thixotropic gel for cleaning metal consisting essentially of bentonite in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, y W t, of the composition; phosphoric acid in amount on an anhydrous basis within the range of about A 5%, by weight, to about 70%, by weight, of the composition; and a corrosion inhibitor within the range of about 0.025%, by weight, to about 0.25%, by weight, of the composition; and a cationic surface active agent within the range of about 2.5%, by weight, to about 8.0%, by weight, of the bentonite present in the composition.

11. A dry powder adapted to form a thixotropic gel suitable for cleaning metal when intimately admixed with an amount of water within the range of about 21.0%, by weight, to about 92.5%, by weight, of the final composition, consisting essentially of bentonite in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of the final composition; oxalic acid in amount on an anhydrous basis within the range of about 5%, by weight, of the composition to the limit of its solubility in the said water, and a water-soluble synthetic organic surfaceactive agent selected from the group consisting of non-ionic and cationic surface active agents and characterized by an essentially linear structure one end of which is hydrophobic and the other end of which is hydrophilic in character, which is solid at normal room temperatures, which is not reactive with the said acid in aqueous solution, which retains its surface activity in the presence of the said aci d and which has the characteristic of synergistically increasing the apparent viscosity of a mixture of bentonite and water, in amount within the range of about 2.5% to about 8.0%, by weight, of the bentonite present in the composition.

12. A composition in the form of a thixotropic gel for cleaning metal consisting essentiall of bentonite in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of

the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of the composition; acetic acid in amount on an anhydrous basis within the range of about 5%, by weight, to about by weight, of the composition; and a water-soluble synthetic organic surface active agent selected from the group consisting of non-ionic and cationic surface active agents and characterized'by an essentially linear structure one end of which is hydrophobic and the other end of which is hydrophilic in character, which is not reactive with the said acid in aqueous solution, which retains its surface activit in the presence or" the said acid and which has the characteristic of synergistically increasing the apparent viscosity of a mixture of bentonite and water, in amount within the range of about 2.5% to about 8.0%, by weight, of the bentonite present in the composition.

13. A composition in the form of a thixotropic gel for cleaning metal consisting essentiall of bentonite in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of

the composition; acetic acid in amount on an anhydrous basis within the range of about 5%, by weight, to about 70% by weight, of the composition; and a water-soluble synthetic organic surface active agent selected from the group consisting of non-ionic and cationic surface active agents and characterized by an essentially linear structure one end of which is hydrophobic and the other end of which is hydrophilic in character, which is not reactive with the said acid in aqueous solution, which retains its surface activity in the presence of the said acid and which has the characteristic of synergistically increasing the apparent viscosity of a mixture of bentonite and water, in amount within the range of about 2.5% to about 8.0%, by weight, of the bentonite present in the composition; and a corrosion inhibitor in amount within the range of about 0.025%, by weight, to about 0.25%, by weight, of the composition.

14. A composition in the form of a thixotropic el for cleaning metal consisting essentiall of bentonite in amount within the range of about 2.5%, by'weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of the composition; acetic acid in amount on an anhydrous basis within the range of about 5%, by weight, to about 70% by weight, of the composition; a corrosion inhibitor within the range of about 0.025%, by weight, to about 0.25%, by weight, of the composition; and a, non-ionic surface active agent within the range of about 2.5%, by weight, to about 8.0% by weight, of the bentonite present in the composition.

15. A composition in the form of a thixotropic gel for cleaning metal consisting essentiall of bentonite in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about v21, by weight, to about 92.5%, by weight, of the composition; acetic acid in amount on an anhydrous basis within the range of about 5%, by weight, to about 70%, by weight, of the composition; lauryl pyridinium chloride within the range of about 0.025%, by weight, to about 0.25%, by weight, of the composition; and a polyoxyethylene ether of an alkyl phenol within the range of about 2.5%, by weight, to about 8.0%,

by weight, of the bentonite present in the composition.

16. A composition in the form of a thixotropic gel for cleaning metal consisting essentially oi? bentonite in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of the composition; phosphoric acid in amount on an anhydrous basis within the range of about by weight, to about 70%, by weight, of the composition; a corrosion inhibitor within the range of about 0.025%, by weight, to about 0.25% by weight, oi the composition; and a non-ionic surface active agent within the range of about 2.5%, by weight, to about 8.0%, by weight, of'the bentonite present in the composition.

1'7. A composition in the form of a thixotropic gel for cleaning metal consisting essentially of bentom'te in amount within the range of about 2.5%, by weight, to about 8.0%, by weight, of the composition; water within the range of about 21%, by weight, to about 92.5%, by weight, of the composition; phosphoric acid in amount on an anhydrous basis within the range of about 5%, by weight, to about 70%, by weight, of the composition; lauryl pyridinium chloride within the References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,428,084 Gravell Sept. 5, 1922 2,220,451 Hunt Nov. 5, 1940 2,396,776 Douty et a1. Mar. 19, 1946 2,516,685 Douty et a1. July 25, 1950 FOREIGN PATENTS Number Country Date 582,139 Germany Aug. 9, 1933 OTHER REFERENCES Triton NEBook1et of Rohm and Haas 00., Philadelphia (1943), pages 3, 4 and 12.

alkyl phenol within the- 

1. A COMPOSITION IN THE FORM OF A THIXOTROPIC GEL FOR CLEANING METAL CONSISTING ESSENTIALLY OF BENTONITE IN AMOUNT WITHIN THE RANGE OF ABOUT 2.5%, BY WEIGHT, TO ABOUT 8.0%, BY WEIGHT, OF THE COMPOSITION; WATER WITHIN THE RANGE OF ABOUT 21%, BY WEIGHT, TO ABOUT 92.5%, BY WEIGHT, OF THE COMPOSITION; AN ACID HAVING AN IONIZATION CONSTANT WITHIN THE RANGE OF ABOUT 1X10-5 TO ABOUT 1X10-2 IN AMOUNT ON AN ANHYDROUS BASIS WITHIN THE RANGE OF ABOUT 5%, BY WEIGHT, OF THE COMPOSITION TO THE LIMIT OF ITS SOLUBILITY IN THE SAID WATER, BUT NOT IN EXCESS OF ABOUT 70%, BY WEIGHT, OF THE SAID COMPOSITION; AND A WATERSOLUBLE SYNTHETIC ARGANIC SURFACE-ACTIVE AGENT SELECTED FROM THE GROUP CONSISTING OF NON-IONIC AND CATIONIC SURFACE ACTIVE AGENTS AND CHARACTERIZED BY AN ESSENTIALLY LINEAR STRUCTURE ONE END OF WHICH IS HYDROPHOBIC AND THE OTHER END OF WHICH IS HYDROPHILIC IN CHARACTER, WHICH IS NOT REACTIVE WITH THE SAID ACID IN AQUEOUS SOLUTION, WHICH RETAINS ITS SURFACE ACTIVITY IN THE PRESENCE OF THE SAID ACID, AND WHICH HAS THE CHARACTERISTIC OF SYNERGISTICALLY INCREASING THE APPARENT VISCOSITY OF A MIXTURE OF BENTONITE AND WATER, IN AMOUNT WITHIN THE RANGE OF ABOUT 2.5% TO ABOUT 8.0% BY WEIGHT, OF THE BENTONITE PRESENT IN THE COMPOSITION. 